Conveyors having conveyor drive rollers which are driven by internal motor/gear combinations are of particular utility in many applications. In these conveyors the motor/gear mechanism is entirely contained within the conveyor drive roll itself. The internal motor/gear system makes for a compact space saving installation. It also greatly reduces maintenance and down time. It virtually eliminates hazards for accidents, and eliminates contamination of the motor/gear drive from dust and debris in the environment in which it is running.
All of these factors make the use of such internal drive conveyors particularly useful and desirable.
Many conveyors are required for continuous, steady speed operation. They are stopped only at the end of a day, or, rarely, for an emergency.
However there are also many applications for such conveyors which require repetitive start/stop/restart operation of the conveyor. This is becoming particularly necessary in the case of luggage conveyors used in the travel industry. In these cases there is a requirement that each piece of luggage has a label printed with the well known Universal Bar Code, (UBC) marking.
This is partly for security reasons, and more importantly for ensuring that the luggage is routed to the correct destination.
It also is of great assistance in identifying a piece of lost luggage.
In order to read the bar code it is necessary that each piece of luggage on the conveyor shall be stationary, for a brief time period.
This in turn means that the conveyor must stop briefly for each individual item, in this case a piece of luggage, to be checked and then restart again, and then stop, and so on, repeatedly.
This is only one example of many applications for conveyors where start/stop/restart operation is required. Such repetitive star/stop/restart operation causes stresses on the drive system. However and more importantly, when the electric drive motor is stopped and restarted, it starts from zero revolutions, and must get up to drive speed in a short time. This causes power surges in the power drawn by the drive motor, which is a well known problem. The power consumption on start up is at least three times, or more, the power consumption at steady state running speed.
The electrical supply to the motor must therefore be capable of carrying excessive currents, simply in order to run the conveyor in such intermittent operations.
Such power surges or “spikes” cause greatly increased charges for power. This is because the power supply to the operator of the conveyor must be adequate to handle the peak power consumption, at these surges, even though when running in steady state the power consumption is only a fraction of the power consumption on start up. The utility company will charge based on power consumption at maximum, rather than average power consumption. Anything that can be done to reduce these power surges or peaks will produce a significant saving in power costs.
Clearly it is desirable to as far as possible reduce these power surges, and to smooth out the power drawn by the motor. This alone will substantially reduce to cost of power for operating the conveyor, and will enable engineers to specify lighter duty wiring and controls for the power supply.
This can be done by the use of a clutch system coupling and uncoupling the motor from the drive roll. The motor can be maintained at regular operational speed, and the conveyor started and stopped by means of the clutch. However building such a motor/clutch combination, operating at a high repetition rate, as is required in the design of a start/stop/start conveyor, such as a luggage conveyor, presents a challenge.
In order to speed up the repetition rate of the start/stop/restart function of the conveyor, driven by such a clutch system, it is also desirable to incorporate an efficient fast acting brake in the system, so as to ensure that when the clutch uncouples from the motor, the conveyor stops almost immediately. The brake must release at once when the clutch is again operated to couple the motor to the conveyor.
Clearly also the clutch must be capable of converting the torque from the motor running at its steady state speed and drive the conveyor from standstill to its designed speed in a brief time period.
All of these factors must be built in to a piece of equipment capable of being installed in the confined space inside the conveyor drive roll itself.